Heretofore, anthraquinone type compounds have been widely utilized in the field of such as dyeing of fibers or as dyestuff and dyes for image formation. On the other hand, in recent years, new color image forming methods such as an inkjet recording method, a thermal transfer method, color electrophotography, printing ink and recording pens are employed in practical use.
As an inkjet recording method, generally utilized are such as a method in which liquid droplets are pressure ejected by means of electromechanical conversion of a piezo element, a method in which liquid droplets are pressure ejected by generated bubbles by means of electro-thermal conversion and a method in which liquid droplets are suction ejected by electrostatic force.
In an inkjet recording liquid (hereinafter, also referred to as inkjet ink or simply as ink), required are such as to suit a recording method selected from those described above, to be provided with a high recording image density and an excellent tone, to be superior in color image fastness such as light fastness, heat resistance and water resistance, to be fixed rapidly to a medium to be recorded and not to bleed, to be excellent in storage stability as ink, to have no problem with respect to safety such as toxicity or inflammability, and to be low-priced.
In these points of view, various inkjet recording liquids have been proposed and examined, however, very few inkjet recording liquids simultaneously satisfy most of the requirements.
In color image recording employing yellow, magenta, cyan and black, widely studied have been conventionally well known dyes and pigments having C. I. numbers, for example, described in C. I. Index. For example, in magenta ink utilizing a water-soluble dye, known are those utilizing xanthene type dyes such as C. I. Acid Red 52 and azo type dyes such as C. I. Direct Red as a water-soluble dye, which are provided with high reliability of anti-clogging in a printer, however, have problems with respect to durability such as light fastness and water resistance. On the other hand, ink employing quinacridone type pigments such as Pigment 122 is known, which is provided with high durability, however, is liable to cause problems of low printing density or poor color reproducibility such as bronzing. In this manner, it has been difficult to simultaneously satisfy both hue and durability, which are required by inkjet ink, with conventionally well known dyes or pigments.
To solve this problem, specific anthraquinone type compounds and water-based ink compositions comprised thereof (for example, refer to patent literatures 1–5) are proposed for the purpose of compatibility of tone and light fastness, however, the level is not sufficient in the rapidly progressing corresponding industry and further improvement has been desired.
On the other hand, in recent years, a proposal, in which water dispersible resin is colored with an oil-soluble dye or a hydrophobic dye, has been made as inkjet recording ink to solve problems of poor water resistance and a poor durability of light fastness in water-based ink utilizing a water-based dye. Proposed are ink comprising an oil-soluble dye being dissolved in a hydrophobic organic solvent having a high boiling point and the resulting solution is dispersed in a water-based medium (for example, refer to patent literature 7), and ink utilizing emulsion polymerized particles or dispersed polymer particles which are dyed with an oil-soluble dye (for example, refer to patent literature 7).
However, ink utilizing an oil-soluble dye is liable to cause aggregation or sedimentation of particles each other resulting in poor stability of ink. Further, it has a problem of hue when being printed as well as a disadvantage of a low printing density, so that further improvement has been required.
[Patent literature 1] JP-A No. 57-195775 (scope of claims, example 3) (Hereinafter, JP-A refers to Japanese Patent Publication Open to Public Inspection)
[Patent literature 2] JP-A No. 59-74173 (scope of claims, example 1)
[Patent literature 3] JP-A No. 2-16171 (scope of claims, example 1)
[Patent literature 4] JP-A No. 10-306221 (scope of claims, example 1)
[Patent literature 5] JP-A No. 2003-192930 (scope of claims, example 5)
[Patent literature 6] JP-A No. 2001-262018 (scope of claims, example 1)
[Patent literature 7] JP-A No. 2001-240763 (scope of claims, example 1)